Fortification of breast milk in VLBW infants: Metabolic acidosis is linked to the composition of fortifiers and alters weight gain and bone mineralization

Summary Background & aims Study objectives were to test (a) whether increased incidence of metabolic acidosis (MA) was caused by introduction of a new commercially available fortifier for breast milk, (b) if so, whether its modification would decrease the incidence of MA and (c) to analyze the impact of MA on growth. Methods Double-blind randomized design. Healthy breast-fed infants (≤34 gestational weeks). Primary outcome measure was incidence of MA (BE  2 , HCO 3 ˉ, electrolytes). Results Part 1 (comparison of standard (SF) and new fortifier (NF)): Interim analysis showed MA in 1 out of 7 (SF) and 7 out of 8 (NF) infants, p  = 0.01; therefore the study was interrupted; subsequently the fortifier was adapted by modifying mineral components. Part 2 (comparison of SF and reformulated fortifier (RF)): MA occurred in 3 out of 15 (SF) and 6 out of 19 (RF), p  = 0.7. When data of all infants studied, those with MA had lower mean weight gain (median: 9 vs. 21 g/kg/d, p p  = 0.04) at discharge. Conclusions When fed fortified breast milk, mild MA spontaneously may develop in 20–30% of VLBW infants. A fortifier with an inappropriate composition may increase the severity and frequency of MA. Our data show that weight gain and BMC seem to be related to acid–base homeostasis. It may be speculated that inadequate growth of fully fed preterm infants is triggered more often by imbalances of acid–base status than previously expected.